Warner Bros. studio on Friday faced the prospect of seeing blockbuster "The Dark Knight Rises" sink at box offices after a tragic movie theater shooting in Denver, even as the film got off to a strong start across the United States and Canada.

Warner Bros., a unit of Time Warner Inc, said the film took in USD 30.6 million at screenings just after midnight, but those results could turn lower in the wake of a mass shooting at one showing of the movie in a Denver suburb.

"The Dark Knight Rises," which is based on the exploits of crime-fighting superhero Batman, is one of this year's major movie releases. Some box office watchers had believed its US and Canadian ticket sales could reach as high as USD 198 million over this debut weekend, just shy of the USD 207 million opening set by "The Avengers" earlier this year. The movie cost Warner Bros. USD 250 million to produce and tens of millions more to market.

But at a midnight premiere in Denver, a gunman wearing a gas mask and a bulletproof vest hurled a gas canister inside the theater and opened fire on moviegoers, killing 12 people and injuring scores more.

Hollywood box office watchers said it was too soon to know exactly how ticket sales would be impacted by the event as the industry has never faced a situation like this one.

"It's too early to tell. This is a tragic and unprecedented event," said Paul Dergarabedian, box office watcher for Hollywood.com Box Office.

Phil Contrino, editor of Boxoffice.com, echoed those sentiments, saying "nobody's ever encountered this before" and added that the first concerns should be for the people and families who were affected by the shooting.

Contrino said the impact on Hollywood and the industry could go beyond just "The Dark Knight Rises" to all films in theaters if people stay away, and it could extend well into the future if the event lingers in people's minds.

Warner Bros. issued the midnight box office number but had nofurther comment. It is the second highest midnight screening total ever, behind 2011's "Harry Potter and the Deathly Hallows - Part II," which raked in $43.5 million in its midnight screenings.

The studio also yanked from theaters the promotional trailer for its upcoming crime thriller "Gangster Squad." Set in the 1940s and 1950s, "Gangster Squad" chronicles the Los Angeles Police Department's fight to keep the mafia out of its city.

The film, which had been playing ahead of "The Dark Knight Rises" in some locations, features a scene in which men open fire with machine guns on an audience in a movie theater.

Elsewhere, the National Association of Theatre Owners, a trade industry association representing movie theater owners, said in a statement its member companies were "working closely with local law enforcement agencies and reviewing security procedures."